Re: sinval synchronization considered harmful

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Noah Misch <noah(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: sinval synchronization considered harmful
Date: 2011-07-27 16:34:35
Message-ID: 10727.1311784475@sss.pgh.pa.us
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Jul 26, 2011 at 9:57 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> 1. Add a new flag to each procState called something like "timeToPayAttention".
>> 2. Each call to SIGetDataEntries() iterates over all the ProcStates
>> whose index is < lastBackend and sets stateP->timeToPayAttention =
>> TRUE for each.
>> 3. At the beginning of SIGetDataEntries(), we do an unlocked if
>> (!stateP->timeToPayAttention) return 0.
>> 4. Immediately following that if statement and before acquiring any
>> locks, we set stateP->timeToPayAttention = FALSE.

> There turned out to be a little bit of further subtlety to this, but
> it seems to work. Patch attached.

And?

It didn't sound to me like this could possibly be a performance win,
but I await some numbers ...

regards, tom lane

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